1. Field of the Invention
The present general inventive concept relates to an image forming apparatus and a method of controlling a fusing unit thereof, and more particularly, to an image forming apparatus improving noises in a standby mode and a method of controlling of a fusing unit thereof.
2. Description of the Related Art
An image forming apparatus includes an image forming unit to develop a visible image corresponding to a wanted image on a printing medium with a toner, and a fusing unit to fuse the toner on the printing medium with heat and pressure. The printing medium passes through the image forming unit and the fusing unit, and then is discharged, thereby completing printing on the printing medium. An electronic copier, a laser printer, a multifunction, etc. belong to the image forming apparatus.
Here, the fusing unit includes a heating roller to accommodate a heat generating member. The heat generating member receives an alternating current power to generate a heat. A pressing roller is included to press the printing medium toward the heating roller. The image forming apparatus includes a power supplying unit to supply the alternating current power to the heat generating member.
To maintain the temperature of the fusing unit within a predetermined objective temperature range, the alternating current power is controlled by two control types, a waveform number control and a phase control.
As illustrated in FIG. 1, the phase control may control the alternating current power by chopping a half wavelength of the alternating current power with respect to a phase thereof and supplying the alternating current power to the heat generating member. As illustrated in FIG. 1, by supplying the alternating current power corresponding to chopped sections A1, A2, A3 and A4 to the heat generating member, the amount of heat generated by the heat generating member is controlled. Here, the sections A1 to A4 represent chopping the half wavelength of the alternating current power by 33%, 50%, 75% and 100% respectively. Here, if the alternating current power supplied to the heat generating member approaches that of an impulse or harmonics near a natural frequency of an element configuring the power supplying unit as the chopped section gets narrower, excessive noise may be caused by resonance.
As illustrated in FIG. 2, the waveform number control may control the number of the waveform of the half wavelength of the alternating current power supplied to the heat generating member, and adopts a waveform of the half wavelength of the alternating current power as a basic unit of a control.
For example, when all of the waveform of the half wavelength alternating current power is supplied, there is a 100% waveform number control. For example, when three waveforms B among four waveforms C are supplied, there is a 75% waveform number control. For example, when a single waveform E among three waveforms D is supplied, there is a 33% waveform number control. For example, when a single waveform G of two waveforms F is supplied, there is a 50% waveform number control. By determining waveforms to be supplied among n waveforms, as exemplified above, the waveform number control is available.
However, in the waveform number control, a large amount of current flows when a power supply starts. This can be referred to as an inrush current The inrush current increases when the fusing unit is designed to generate more heat, such as when there are a plurality of heat generating members. This excessive inrush current causes an excessive voltage variation, and accordingly, a flicker phenomenon may be caused, which is known as the turning on and off of a lamp. The flicker phenomenon may cause a malfunction of the fusing unit, and may even damage a circuit in the power supplying unit.